This invention relates to the art of post-mix beverage dispensers and, more particularly, to improved valves for obtaining a constant flow rate with respect to diluents and syrups which are mixed to produce the beverage to be dispensed. Post-mix beverage dispensers are of course well known and, generally, are basically of the structure and operation shown in U.S. Pat. No. 4,266,726 to Brown et al, the disclosure of which is incorporated herein by reference for background purposes. In a post-mix dispenser of the foregoing character, a diluent such as soda water and a syrup flow into the body of the dispenser through separate inlet passageways and across corresponding flow rate control valves toward a mixing area which is generally associated with the nozzle of the dispenser. Flow through the nozzle is generally controlled by a pair of solenoid valves, one for each of the liquids. A drink is dispensed by pressing a receptacle such as a cup against a control lever adjacent the dispensing nozzle which actuates a microswitch which in turn actuates the solenoid valves simultaneously for the diluent and syrup to flow into and through the nozzle and into the receptacle. The syrup and diluent are fed to the inlet ends of the flow passageways from separate sources under pressure and, upon opening of the solenoid valves, the liquids flows through the corresponding flow rate control valve to the dispensing nozzle.
It is of course well known that in post-mix beverage dispensers, the flow rates of the diluent and syrup streams must be regulated so that the finished drink contains the proper ratio of diluent to syrup. The pressures of the diluent, which is most often soda water, and the syrup vary with respect to time and temperature and, therefore, the valves which control the soda water and syrup flow rates must be able to provide a constant flow rate for the corresponding liquid under varying pressure conditions. In addition to being operable under varying pressure conditions, it is also desirable to provide for the flow rate controlling valves to be operable at a variety of different flow rates. As is also well known, the viscosity of soda water is lower than that of the syrups to be mixed therewith in forming a beverage and, with respect to syrups, syrups for diet drinks are of a lower viscosity than those for regular or non-diet drinks. It will be appreciated, therefore, that the valves controlling the soda water and syrup flow rates have to be operable with liquids of different viscosity.
One type of flow rate controlling valve heretofore employed in connection with post-mix dispensers is shown in the aforementioned patent to Brown et al and, basically, comprises a spring biased piston reciprocable in a cylinder assembly and having an orifice through which the liquid flows into the cylinder assembly. The cylinder assembly has outlet ports adjacent the inner end of the piston and which are controlled by displacement of the piston in the cylinder. More particularly in this respect, liquid under pressure flows through the orifice and, above a predetermined pressure, displaces the piston against the biasing spring force. As the pressure of the liquid increases and decreases relative to the predetermined pressure, the piston will respectively decrease and increase the size of the outlet ports, thus to maintain a constant flow rate under variable pressure conditions. While flow control valves of this character serve their intended purpose, the range of operation thereof with respect to providing a variety of flow rates and liquid viscosity ranges under which they are operable is limited by the size of the orifice in the piston, the adjustability of the spring force and the stroke of the piston with respect to controlling the outlet ports of the valve. Accordingly, it is very difficult to provide one valve configuration which will regulate liquid flow accurately over both a desired flow rate and viscosity range. Thus, separate flow control valve configurations with respect to piston orifice, spring force and outlet port size have been required to obtain desired flow rates for given liquid viscosities and pressure variations. The necessity of providing a variety of flow rate control valve configurations is of course expensive and inconvenient and, at least partially in this respect, requires maintaining a rather large inventory of component parts which are appropriately identified to assure assembly of the appropriate parts to provide a valve having the desired flow rate controlling capability.
Another disadvantage in conjunction with flow rate controlling valves of the piston-cylinder type referred to above resides in the fact that the cylinder assembly is defined by coaxial sleeve and bonnet components including an accurately machined metal sleeve in which the piston is reciprocable and which includes the outlet ports controlled by the piston during operation of the valve. The bonnet supports a spring adjusting device by which the spring force against the piston is adjustable, and the bonnet also serves in conjunction with an appropriate retainer to removably secure the valve in an opening therefor in the dispenser body. In order for the valve to accommodate different flow rates and liquid viscosities, the machined sleeves are provided with different sized outlet ports, thus requiring a high inventory of sleeves to enable the assembly of valves having a variety of flow rate and viscosity handling capabilities. Again, this requirement adds to the manufacturing and maintenance costs in connection with post-mix dispensers.